/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
 *
 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util;

/**
 * This class provides skeletal implementations of some {@link Queue}
 * operations. The implementations in this class are appropriate when
 * the base implementation does <em>not</em> allow <tt>null</tt>
 * elements.  Methods {@link #add add}, {@link #remove remove}, and
 * {@link #element element} are based on {@link #offer offer}, {@link
 * #poll poll}, and {@link #peek peek}, respectively, but throw
 * exceptions instead of indicating failure via <tt>false</tt> or
 * <tt>null</tt> returns.
 *
 * <p>A <tt>Queue</tt> implementation that extends this class must
 * minimally define a method {@link Queue#offer} which does not permit
 * insertion of <tt>null</tt> elements, along with methods {@link
 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
 * {@link Collection#iterator}.  Typically, additional methods will be
 * overridden as well.  If these requirements cannot be met, consider
 * instead subclassing {@link AbstractCollection}.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements held in this collection
 * @author Doug Lea
 * @since 1.5
 */
public abstract class AbstractQueue<E>
    extends AbstractCollection<E>
    implements Queue<E> {

  /**
   * Constructor for use by subclasses.
   */
  protected AbstractQueue() {
  }

  /**
   * Inserts the specified element into this queue if it is possible to do so
   * immediately without violating capacity restrictions, returning
   * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
   * if no space is currently available.
   *
   * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
   * else throws an <tt>IllegalStateException</tt>.
   *
   * @param e the element to add
   * @return <tt>true</tt> (as specified by {@link Collection#add})
   * @throws IllegalStateException if the element cannot be added at this time due to capacity
   * restrictions
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this queue
   * @throws NullPointerException if the specified element is null and this queue does not permit
   * null elements
   * @throws IllegalArgumentException if some property of this element prevents it from being added
   * to this queue
   */
  public boolean add(E e) {
    if (offer(e)) {
      return true;
    } else {
      throw new IllegalStateException("Queue full");
    }
  }

  /**
   * Retrieves and removes the head of this queue.  This method differs
   * from {@link #poll poll} only in that it throws an exception if this
   * queue is empty.
   *
   * <p>This implementation returns the result of <tt>poll</tt>
   * unless the queue is empty.
   *
   * @return the head of this queue
   * @throws NoSuchElementException if this queue is empty
   */
  public E remove() {
    E x = poll();
    if (x != null) {
      return x;
    } else {
      throw new NoSuchElementException();
    }
  }

  /**
   * Retrieves, but does not remove, the head of this queue.  This method
   * differs from {@link #peek peek} only in that it throws an exception if
   * this queue is empty.
   *
   * <p>This implementation returns the result of <tt>peek</tt>
   * unless the queue is empty.
   *
   * @return the head of this queue
   * @throws NoSuchElementException if this queue is empty
   */
  public E element() {
    E x = peek();
    if (x != null) {
      return x;
    } else {
      throw new NoSuchElementException();
    }
  }

  /**
   * Removes all of the elements from this queue.
   * The queue will be empty after this call returns.
   *
   * <p>This implementation repeatedly invokes {@link #poll poll} until it
   * returns <tt>null</tt>.
   */
  public void clear() {
    while (poll() != null) {
      ;
    }
  }

  /**
   * Adds all of the elements in the specified collection to this
   * queue.  Attempts to addAll of a queue to itself result in
   * <tt>IllegalArgumentException</tt>. Further, the behavior of
   * this operation is undefined if the specified collection is
   * modified while the operation is in progress.
   *
   * <p>This implementation iterates over the specified collection,
   * and adds each element returned by the iterator to this
   * queue, in turn.  A runtime exception encountered while
   * trying to add an element (including, in particular, a
   * <tt>null</tt> element) may result in only some of the elements
   * having been successfully added when the associated exception is
   * thrown.
   *
   * @param c collection containing elements to be added to this queue
   * @return <tt>true</tt> if this queue changed as a result of the call
   * @throws ClassCastException if the class of an element of the specified collection prevents it
   * from being added to this queue
   * @throws NullPointerException if the specified collection contains a null element and this queue
   * does not permit null elements, or if the specified collection is null
   * @throws IllegalArgumentException if some property of an element of the specified collection
   * prevents it from being added to this queue, or if the specified collection is this queue
   * @throws IllegalStateException if not all the elements can be added at this time due to
   * insertion restrictions
   * @see #add(Object)
   */
  public boolean addAll(Collection<? extends E> c) {
    if (c == null) {
      throw new NullPointerException();
    }
    if (c == this) {
      throw new IllegalArgumentException();
    }
    boolean modified = false;
    for (E e : c) {
      if (add(e)) {
        modified = true;
      }
    }
    return modified;
  }

}
